In recent years, as a mobile station represented by a mobile phone system, a PHS (Personal Handy phone System), and a PDA (Personal Digital Assistant) have been provided. These mobile stations are capable of conducting communication such as making and receiving a call and transmitting and receiving data by accessing base stations installed with a predetermined distance from one another through a communication network accessed by the base stations.
One of schemes used for such a wireless communication system to transmit a digital signal is an OFDM modulation scheme. Since an OFDM modulation scheme transmits transmission data by distributing them to a plurality of carriers, in which orthogonal frequencies are set, a band of each of the carriers becomes narrow, so that frequency use efficiency is very high.
In addition, as shown in FIG. 12, the OFDM modulation scheme is composed of an effective symbol corresponding to a signal period, during which IFFT (Inverse Fast Fourier Transformation) is performed at the time of transmission, and a guard interval 50 obtained by copying the waveform of a part of the latter half of the effective symbol as it is. For example, if the effective symbol length is 512 samples, the guard interval 50 is 64 samples, which is ⅛ of the effective symbol length. And, the guard interval 50 is inserted into a former half of an OFDM symbol. In the OFDM modulation scheme, the insertion of the guard interval 50 permits inter-symbol interference due to multipath, and thereby enhancing the resistance against multipath.
On the other hand, in a wireless communication system of PHS, communication is possible by transmitting and receiving a notification channel (BCCH: Broadcast Control Channel) between the base stations (CS: Cell Station) and the mobile stations (PS: Personal Station) arranged within a service area and assigning a communication channel (TCH: Traffic Channel), at the time of an outgoing call, an incoming call, location registration, and others.
In order to establish such a communication channel, it is necessary to correct transmission timing of a mobile station to be synchronized with reference timing of a base station. To generally explain the flow, firstly, the mobile station generates a channel for timing correction and transmits an OFDM symbol to the base station. The base station detects timing by using the received OFDM symbol and notifies the mobile station of a differential from reference timing of the base station. The mobile station corrects transmission timing to solve the differential from the reference timing.
The mobile station sends a communication channel assignment request for making an outgoing call to the base station at the corrected transmission timing. Upon receiving this request, the base station transmits communication channel assignment information to the mobile station (for example, Patent Literatures 1 to 4).    Patent Literature 1: JP-A-2000-68972    Patent Literature 2: JP-A-2000-134176    Patent Literature 3: JP-A-2000-315991    Patent Literature 4: JP-A-2001-119368